1. Field of the Invention
This invention relates to position detection, and more particularly to a position detecting method and a position detecting system.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional passive-type digital tablet pointing system disclosed in U.S. Pat. No. 7,176,907 is shown to include a digital tablet 1 and a wireless pointing device 2 (e.g., a digital stylus).
The wireless pointing device 2 is operable to obtain energy from an external signal upon receipt of the external signal, and then to transmit, in response to the external signal, a signal having an oscillation frequency using the energy obtained thereby. The wireless pointing device 2 includes a variable inductor 21, two capacitors 22, 23, and a switch 24. Inductance of the variable inductor 21 decreases with increasing contact pressure between the wireless pointing device 2 and the digital tablet 1 to thereby increase the oscillation frequency. When the switch 24 conducts, the capacitor 23 causes the oscillation frequency to decrease.
The digital tablet 1 includes a plurality of first antennas 11 arranged in a first direction, and a plurality of second antennas 12 arranged in a second direction perpendicular to the first direction. The digital tablet 1 is operable, via all or a group of the first and second antennas 11, 12 successively, to continuously transmit to the wireless pointing device 2 an excitation signal having a constant frequency and then to receive a response signal, which is transmitted from the wireless pointing device 2 in response to the excitation signal, so as to perform full-region or sub-region scanning. The digital tablet 1 is further operable to obtain, based on an energy level of the response signal, position information corresponding to a position that is indicated by the wireless pointing device 2 and that is relative to the digital tablet 1, and to obtain, based on a frequency of the response signal, state information associated with the wireless pointing device 2 (e.g., the contact pressure between the wireless pointing device 2 and the digital tablet 1, and operation state of the switch 24).
However, the conventional digital tablet pointing system has the following drawbacks:
1. The position information and the contact pressure obtained by the digital tablet 1 have relatively low precision. The operation state of the switch 24 obtained by the digital tablet 1 may be inaccurate.
2. The digital tablet 1 uses a relatively large number of switches 13 for the first and second antennas 11, 12, respectively.
3. Moreover, a frequency/voltage conversion circuit 14 is required for the digital tablet 1 to generate the state information.